The present invention relates to a fire-retardant composition, and in particular, to a corrosion-inhibited ammonium polyphosphate fire-retardant composition.
Ammonium polyphosphate fire-retardant compositions are widely used to effectively combat the spread wildland fires. Typically, ammonium polyphosphate fire-retardants are supplied and stored in tanks as a concentrated suspension or slurry. In the event of a fire, the stored ammonium polyphosphate fire-retardant is diluted and transported using fixed-wing aircraft or helicopters for aerial application to the fire. However, ammonium polyphosphate can be extremely corrosive to aluminum, carbon steel, brass, and magnesium. It is therefore necessary to corrosion inhibit the ammonium polyphosphate fire-retardant to protect the equipment used to produce, store, handle and apply the ammonium polyphosphate fire-retardant.
It is known that iron additives may reduce the corrosiveness of ammonium polyphosphate fire-retardants to aluminum. This is disclosed in U.S. Pat. Nos. 6,620,348 and 6,846,437 to Vandersall et al., and U.S. Pat. No. 6,802,994 to Kegler et al., all of which are incorporated herein by reference. However, certain iron additives, in the form of dissolved salts, are oxidizers and can increase the corrosiveness of the ammonium polyphosphate fire-retardants to carbon steel. As such, carbon steel tanks used to store ammonium polyphosphate fire-retardants with iron additives require an epoxy coating to protect against corrosion. There is therefore a need for an improved corrosion-inhibited ammonium polyphosphate fire-retardant composition.